Mud, you don't need to "save" it on your own.. the Duenna program does it for you.
At the end of the flight it should pop up both the .txt file and the .jpg Close both and they are saved in the "Output" folder (C:/program files/fsaddons/RTW_Duenna/Output/). The popup may show Map Unavailable but it should still produce the file.
Take a look in that folder and you should have two files of each name (one .txt. and one .jpg. When you make your post, browse to and attach both files. (takes two separate attachments of course).
If your Output folder doesn't have the .jpg file then let us know and we can do some more digging.
For now, until the race, go to settings and in the lower half of the page, de-select "Send realtime position to server" and select "Keep flight tracking private". Tha way it won't get set to the RTW tracking site to show what you're doing. When it's the race that will have to be changed to allow you to be "followed"
As Gnoopey says, you need the full-install Duenna and the Update release 117 to be current.
Rob